The present invention relates generally to the preparation of phenolic and aromatic amine polymers, wherein the reaction conditions are controlled such that high product yields, molecular weight, and a uniform molecular weight distribution are obtained.
Phenolic and aromatic amine polymer resins constitute a very important and useful class of chemical compounds. They have a number of uses, e.g., as coatings and laminates that provide a number of functional advantages. Besides possessing good thermal properties, these polymers can be doped to make them electrically conductive, making them a key component of integrated circuit (IC) chips.
At present, these polymers are prepared by chemical synthesis, e.g., as from phenol and formaldehyde. The polymers""s linearity/network structure (and, by extension, their functional properties) varies depending on the monomer and type of reaction conditions used. However, the use of certain constituent chemicals, such as formaldehyde, is being restricted in the chemical industry because of their toxicity. Accordingly, the enzyme-mediated synthesis of polyphenols and polyaromatic amines offers a viable alternative to the currently used chemical synthesis of such commercial phenolic resins.
Peroxidase-catalyzed free radical polymerization of phenol, aromatic amines, and their derivatives is well known. Horseradish peroxidase (HRP) is the most widely used biocatalyst in the polymerization of phenol, aniline, or their derivatives. HRP has been shown to be active in a number of organic solvents or solvent mixtures and the reaction is typically initiated by the addition of hydrogen peroxide as an oxidant.
Dordick et al., Vol. # 30 1987 Biotechnol. Bioeng. 31-36, used HRP in a dioxane/water system to prepare a number of polymers and copolymers from various phenolic monomers. Akkara et al., 29 J. Poylm. Sci. A 1561 (1991), prepared polymers and copolymers of various phenols and aromatic amines using these same reactions and carried out detailed characterization of the polymer products. p-Alkylphenols were also polymerized at oil-water (reversed micelles) and air-water (Langmuir-Blodgett trough) interfaces. Because of their amphiphilic nature, the alkylphenols are positioned at the interface, and in the presence of HRP and hydrogen peroxide the monomers are oxidatively coupled to form polymers. The poly(p-alkylphenols) prepared in reversed micelles were shown to exhibit relatively more uniform molecular weight distribution than those prepared in bulk organic solvents.
However, earlier attempts to control the polymer molecular weight and molecular weight distribution by varying the time of reaction or hydrogen peroxide concentration were unsuccessful in both reversed micelles and bulk solvents. Initial hydrogen peroxide concentration was found to be stoichiometrically proportional to the monomer conversion, a hallmark of stepwise polymerization and a phenomenon observed previously, and there was no effect on the polymer molecular weight and polydispersity.
The polymers can be modified by adding functional groups to the polymeric backbone, significantly enhancing the utility of these polymers. xe2x80x9cFunctionalizationxe2x80x9d enables the polymers to be used to treat fabrics, to form selectively permeable membranes, and to improve the performance of IC chips, among other applications.
Palmitoyl chlorides may be added to the polymer to make the polymer easily processable, e.g., as coatings, films, or finishes. Cinnamoyl chloride may be added to create controlled pore size membranes (e.g., xe2x80x9cmolecular sievesxe2x80x9d) or to enhance the polymers""s ability to absorb UV radiation (e.g., for sunglasses), thereby enabling their use as anti-reflective coatings in photoresists. In their latter use, the modified polymers are applied to a silicon substrate as an undercoating (under non-functionalized polyphenols or polyaromatic amines that are then applied as a spin coating) in an IC chip to control the precision of UV etching, by inhibiting UV scattering, of circuitry into the spin-coated polymer layer. In addition, these cinnamoyl chloride-modified polymers are very thermostable, which allows their use in a variety of applications where heat is ordinarily a problem. In contrast, photosensitive functional groups may be added to enhance the utility of the polymers in other applications.
The polymers also may be modified to create active matrices and systems allowing the controlled-release of materials, such as drugs, insecticides, and fertilizers If biotin groups are added to the polymer chain, the polymer can be used as chromatography packing, which may be used to separate and purify proteins.
Despite the study of how the functionality of the polymers varies depending upon whether, and with what, the molecules are modified, it has not been shown that the molecular weight and the molecular weight distribution (i.e., the xe2x80x9cpolydispersityxe2x80x9d) of polyphenols and polyaromatic amines also can significantly influence the functional properties of the polymers.
Accordingly, it is an object of this invention to overcome the above illustrated inadequacies and problems of extant polyphenols and polyaromatic amines by providing an improved method of their manufacture suitable for use in applications that would benefit from uniform polymer size.
It is another object of this invention to provide a method of producing polyphenols and polyaromatic amines wherein it is possible to control the molecular weight distribution of the polymer molecules.
Yet another object of the present invention is to provide a method of producing polyphenols and polyaromatic amines wherein the molecular weight distribution of the polymer molecules is between 600 and 3,600.
It is a further object of the present invention to provide a method of producing polyphenols and polyaromatic amines wherein the molecular weight distribution of the polymer molecules is between 1,400 and 25,000.
A still further object is to provide a method of producing polyphenols and polyaromatic amines wherein it is possible to control the polydispersity of the polymer molecules.
It is another object of this invention to provide a method of producing polyphenols and polyaromatic amines wherein the polydispersity of the polymer molecules ranges from 1.02 to greater than 2.
It is yet another object of the present invention to provide a method to modify the polymer prepared by adding functional groups to the polymer using palmitoyl chloride, cinnamoyl chloride, and biotin compounds.
The objects of the present invention are met by a method of enzymatically synthesizing polyphenols and polyaromatic amines under controlled reaction conditions. More particularly, the invention relates to the control of molecular weight and polydispersity in enzymatically synthesized polyphenols and polyaromatic amines by manipulating the several reaction parameters.
The present invention defines reaction conditions for any given phenol/aromatic amine monomer necessary to control Mw and polydispersity within a defined range. Such control of Mw and polydispersity has been found to increase the utility of these polymers.
In particular, the ability to control the molecular weight and dispersity of poly(p-ethylphenol) and poly(m-cresol) has been achieved. The polymers were synthesized enzymatically in different organic solvents and a water-in-oil microemulsion. Using solubility parameters, the composition of the reaction medium was varied to study the effects on polymer yield, molecular weight, and dispersity. It has been discovered that polymers with low dispersities and with molecular weights ranging from 1000 to 3000 can be synthesized in reversed micelles. In addition, it has been discovered that reactions conducted in bulk solvents resulted in a narrow range of molecular weights (281 to 675 with poly(p-ethylphenol) in a dimethylformamide (DMF)/water system and 1,400 to 25,000 with poly(m-cresol) in an ethanol/water system).
With DMF as the chromatography eluent, the effect of LiBr in DMF on the molecular aggregation of poly(p-ethylphenol) was determined using gel permeation chromatography (GPC). The presence of LiBr (at 0.35 w/v %) in DMF resulted in complete dissociation of the aggregates in solution. Further, poly(p-ethylphenol) was functionalized at hydroxyl positions with palmitoyl and cinnamoyl groups. Structural characterization of the polymers was carried out by 13C-NMR, UV, and FTIR spectroscopies.
Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings.